The HDC1000EVM evaluation board

As is often the way these days, Texas make a nice evaluation board the HDC1000EVM2 which is essentially the HDC1000 sensor chip plus a M430F55283 microcontroller which connects the I²C interface on the sensor to USB.

A bit of probing reveals that, by default the onboard sensor has I²C address 0x40.

Watching the I²C bus also reveals that when power is applied to the board, it sends a software reset, then enables 14-bit conversions of temperature and relative humidity. The precise commands are:

0x80, 0x00;

0x10, 0x00.

Terminal interface

On Windows you can download client software which talks to the evaluation board. However, I use a Mac. Happily the board appears as a serial device in /dev e.g. /dev/tty.usbmodem146151.

Opening the device with screen and prodding keys reveals that most of the numbers do something:

1: return the undecoded temperature in hex;

2: return the undecoded relative-humidity in hex;

3: start streaming temperature and RH readings;

4: stop streaming;

5: decrement the time between measurements when streaming;

6: increment the time between measurements when streaming;

7: cycles 0,1,2,3—it’s not clear what this changes;

8: cycle the I²C address used: 0x40, 0x41, 0x42, 0x43.

A reasonable strategy for logging over time is to periodically send ‘1’ and ‘2’, logging the results. If precise timing doesn’t matter though, we can just stream the data.